Level sensing instruments are used for sensing level of a process fluid in a process vessel. Many such instruments are of the intrusive type in which a sensing apparatus is exposed to the process fluid for sensing level. One such type of intrusive instrument comprises a magnetostrictive sensor. A magnetostrictive sensor has a magnetostrictive wire assembly including a magnetostrictive wire maintained under tension in a tube. The tube extends into the process vessel. A magnetic float is captured on the tube and floats atop the fluid in the vessel. An electrical pulse is transmitted on the magnetostrictive wire. The electrical pulse interacts with the magnetic field of the float, which creates a torque on the wire to cause an acoustic pulse to be sent on the wire. The time of flight between the transmission of the electrical pulse and the receipt of the acoustic pulse is sensed for determining distance of the process fluid from the instrument, representing level. With such a magnetostrictive level sensing instrument, the tube is mounted to an electronics housing. The housing is in turn connected to a process fitting installed in an opening in the vessel.
In a typical application, a process vessel includes an opening into a storage space in the vessel. In high pressure, high temperature, or explosive environments, it is desirable to maintain the process sealed. Such an opening can be sealed simply by installing the particular level sensing instrument. However, when the instrument, in this case the magnetostrictive wire assembly, must be removed for servicing or replacement, the seal is broken. Advantageously, the mounting arrangement would include a process seal which need not be interfered with in order to service or replace the level sensing instrument.
The present invention is directed to solving one or more of the problems discussed above in a novel and simple manner.